The location and geological history of New Caledonia has made this Pacific island one of the most intriguing spots on earth to study plant evolution. The island separated from Australia roughly 65 mya, carrying with it many ancient lineages of angiosperms, some of which are left nowhere else on earth (e.g., Amborella). Although its tectonic history has predisposed this island to high levels of paleoendemism, the unique combination of geography, geology, and ecology found in New Caledonia has also provided many opportunities for more recent speciation. Araliaceae have a near-cosmopolitan distribution, but their generic and species diversity is nowhere greater than in New Caledonia, making the family an ideal model for studying both paleo- and neoendemism. To infer the role of geological history and physical conditions on evolutionary patterns, we present data on three araliad lineages. The generic diversity of one lineage (comprising Mydocarpus, Delarbrea, and Pseudosciadium) appears to pre-date the late Cretaceous separation of New Caledonia from Australia, but species diversity is likely due to radiations onto ultramafic substrates, especially in Myodocarpus. For two other araliad lineages, Polyscias and Schefflera, our data suggest an arrival in New Caledonia via long-distance dispersal (most likely after the Cretaceous), followed by relatively recent radiations. Speciation patterns in these genera, especially in Polyscias, are closely correlated with the physical diversity of the island. Species pairs that are morphologically coherent and yet clearly distinguishable are allopatrically isolated on the basis of elevation, soil types, and/or local geography. The single species Polyscias dioica, however, combines high levels of morphological variability and a broad distribution across the island with complex patterns of phylogenetic relationships. Species "breakdown" (via hybridization among once distinct species) may account for this exceptional pattern.

Key words: Araliaceae, molecular systematics, Myodocarpus, New Caledonia, Polyscias, Schefflera